Today is Spain's National Day, the Fiesta Nacional. And it comes in the middle of a major constitutional crisis in Spain. The region of Catalonia is led by separatists who held a disputed referendum earlier this month. They say the results give them a mandate to break away. Now the Spanish government is threatening to depose the Catalan leadership. Lauren Frayer reports from Madrid.

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LAUREN FRAYER, BYLINE: Spanish soldiers fired cannons into the air as the king inspected troops. A paratrooper descended from the sky, trailing a giant Spanish flag.

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FRAYER: It was the first time in years almost the entire Spanish government showed up for the National Day Parade. Dignitaries spoke of unity, a veiled reference to the word they did not utter.

FRAYER: "This parade is a show of the strength we can mobilize," he says, "to prevent the breakup of our country." He hopes it doesn't come to that.

Spanish Prime Minister Mariano Rajoy has issued an ultimatum. The Catalan separatist leader, Carles Puigdemont, has until Monday to clarify whether or not he has declared independence and until next Thursday to change his mind if he has. Otherwise Rajoy will invoke Article 155 of the Spanish Constitution, deposing Catalonia's entire regional government. In Catalonia today, there were noisy protests...

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UNIDENTIFIED PROTESTERS: (Chanting in Spanish).

FRAYER: ...By Catalans who want to stay part of Spain.

TERESA: I'm so proud to be Catalan, but I'm so proud to be Spanish - both of them.

FRAYER: Teresa didn't want to give her last name. Talking politics in the street is sensitive these days. She's Catalan, and she wants Spain to use its constitution to punish Catalan leaders, whom she blames for this crisis.

TERESA: This is the worst it could be. And if they don't want to be in the law, sorry, but this is the only way. The constitution all these years have been in our country, Spain.

FRAYER: Puigdemont has not replied to Rajoy's ultimatum except for on Twitter, where he wrote, I ask for dialogue and they put Article 155 on the table. Understood. Rajoy is taking a hard line, and Europe has not come to Puigdemont's rescue. It considers all of this an internal Spanish matter. But there are signs of a possible compromise revealed last night by Spain's opposition socialist leader, Pedro Sanchez.

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PEDRO SANCHEZ: (Speaking Spanish).

FRAYER: "The time has come to reform the Spanish Constitution," he said, announcing an agreement with Rajoy's government. Over the next six months, a bipartisan group of lawmakers will study how to change the relationship Spain has with its autonomous regions to prevent a case like Catalonia from happening again, possibly to give the regions more powers over taxation and spending, which Catalonia has long demanded. That is a six-month process. Spain must first get through the next few days. For NPR News, I'm Lauren Frayer in Madrid.